The present invention relates generally to antennas, and more specifically to switched beam antennas, beam scanning antennas, and smart antennas. Such antennas are used, for example, in cellular or radio-frequency communication systems, indoor local area networks, military and surveillance applications, radars, and numerous other applications.
The two main components in a cellular, or radio frequency, communications system are the base station and the mobile station. In typical cellular systems, geographically defined areas are referred to as cells, and there is one base station in each cell. All mobile stations that are within the cell, communicate with the base station. The mobile stations communicate wirelessly with the base station, and the base station interfaces with a wired network for continued communications over the Internet, or over the plain old telephone system (POTS). The mobile stations communicate with the base station until they leave the geographical area defined by the cell. When the mobile station travels outside of the cell, the mobile station enters the range of another cell and starts communicating with another base station through a procedure known as hand-off, which occurs between the old and new base stations.
New cellular communication systems are finding use in smaller areas, such as indoors, and are being asked to handle more subscribers. Demands for low cost, high quality, robust and high data rate communication systems are increasing rapidly. Fortunately, wireless communication technology continues to grow quickly. Novel technologies have been employed to enhance the quality and functionality of these wireless systems. One of these novel technologies which has been employed recently and received lots of attention are beam switching antennas. Beam switching antennas are one of the smart antenna technologies and have found use in recent wireless communication systems. They allow for energy savings, decreasing multipath fading by directing the desired signal toward the appropriate user, and adding more flexibility to the antenna, thereby, increasing functionality of the antenna, leading to good transmission quality.
There are various methods for designing beam switching antennas. For instance, a conventional phased antenna array was a promising solution for beam switching and beam steering applications. However, complex power distribution networks and phase shifters are needed which greatly increases the size and price of such designs. Another attempted solution is using a Butler matrix, but integration of the matrix with an antenna array also is complex, requiring a large amount of space and inflating the price. Recently, active EBG structures have been used for designing reconfigurable antennas with switching characteristics. However, these systems employ a large number of active elements which increases power consumption, cost, complexity of the fabrication and maintenance.